Artificial incoherent speckles enable precision astrometry and photometry in high-contrast imaging

TL;DR

This paper introduces a novel method using deformable mirrors to generate incoherent speckles in high-contrast imaging, significantly enhancing the precision of astrometry and photometry for exoplanet observations.

Contribution

The study demonstrates a new speckle calibration technique that improves the robustness and stability of adaptive optics imaging by modulating speckle phase to achieve incoherence.

Findings

Speckles can be placed up to 22.5 λ/D from the star.

Fast phase modulation renders speckles effectively incoherent.

Incoherence increases calibration robustness and stability.

Abstract

State-of-the-art coronagraphs employed on extreme adaptive optics enabled instruments, are constantly improving the contrast detection limit for companions at ever closer separations to the host star. In order to constrain their properties and ultimately compositions, it is important to precisely determine orbital parameters and contrasts with respect to the stars they orbit. This can be difficult in the post coronagraphic image plane, as by definition the central star has been occulted by the coronagraph. We demonstrate the flexibility of utilizing the deformable mirror in the adaptive optics system in SCExAO to generate a field of speckles for the purposes of calibration. Speckles can be placed up to $22.5~\lambda/D$ from the star, with any position angle, brightness and abundance required. Most importantly, we show that a fast modulation of the added speckle phase, between $0$ and $\pi$, during a long science integration renders these speckles effectively incoherent with the underlying halo. We quantitatively show for the first time that this incoherence in turn, increases the robustness and stability of the adaptive speckles which will improve the precision of astrometric and photometric calibration procedures. This technique will be valuable for high-contrast imaging observations with imagers and integral field spectrographs alike.